Who will buy Skype? Yahoo!? or Google? or Rupert Murdoch?

Rumours of a Skype valuation of $3bn Rupert Murdoch's New International from columnist Bob Cringeley, dismissed by another columnist (Simon Edhouse of Virtusoft) have surfaced - but is Skype a valuable commodity, then?

The question has hidden answers, because most of the people who are likely to be interested in Skype are not yet showing their hands in the marketplace.

Specifically, two companies have leaked drips of information about their telephony plans: Google and Yahoo! are both known to be planning a complete package.

In the case of Google, nothing has been confirmed, but advertisements have been seen for the sort of people who are needed to manage a combined wireline, gateway, mobile and wireless IP phone network.

In the case of Yahoo! even less has been published, but again, preparations have been apparent from hirings of staff and purchases of equipment.

Both companies would be crucially handicapped if the other bought Skype, and really, the only reason either might fail to buy the peer-to-peer phone network, would be either that they came second in the race, or that Skype really didn't want to sell.

What is Skype worth? Cringeley says Murdoch offered $3bn; there's no validation of this news. But (says Bloomberg) Tim Draper, managing director of venture capital firm Draper Fisher Jurvetson, "compares Skype to free email company Hotmail, purchased by Microsoft in 1998 for US$450m and now boasting 190 million users. He calls Skype a classic disruptive technology."

Draper, apparently, thinks $3bn is peanuts, and is thinking more in terms of $100bn - hard to relate, in accounting terms, to any sort of projected revenue Skype might ever make.

The analysis is all based on the assumption that Skype faces no rivals, no technical challenges. This is almost certainly wide of the mark.

In terms of rivals, Microsoft's MSN is already close to achieving a profile with its MSN Messenger which has good credibility as a telephony provider; Yahoo's instant messenger service is less credible as a voice carrier, but that will all change before the end of this year, when it unveils its plans in mobile and VoIP telephony.

In terms of technology, Skype has a real problem: it relies on "supernodes" - users who have direct Web access to a "real" IP address. The traffic in and out of normal nodes wouldn't be capable of travelling between two subscribers; there are no inbound routes. So the software fakes a session through a supernode.

The problem seems to be: the number of potential supernodes is dropping, and the number of ordinary nodes - behind mapped addresses or firewalls, or both - is going up rapidly.

The result: quality of calls is falling. Bandwidth available is poor compared with a year ago.

This problem is one Skype may solve before it becomes visible to potential buyers. If it thinks the solution is easy, it has no need to rush to accept a suitor.

So: if Cringeley's rumour is right, then the next two weeks will show how optimistic Skype founder Niklas Zennström is. If he sells out before September, we can deduce he's not sure about being able to solve the technical challenge. If he hangs on, we can suspect he's got it cracked.